Adenine is widely present in the tissues of animals and plants as a main constituent of nucleic acids and coenzymes. Adenine and its derivatives also are known as having pharmacological effects and are very useful in the medical and biochemical fields.
There are serval known methods for producing adenine. For example, U.S. Pat. No. 3,287,452 discloses a method of producing adenine and 4,5-dicyanoimidazole which comprises reacting a source of hydrogen cyanide with ammonia in the liquid state in the absence of an amount of water greater than ten mole percent of the combined amounts of the hydrogen cyanide and the ammonia at a temperature of 60.degree. C. to 150.degree. C., wherein the mole ratio of ammonia to hydrogen cyanide is at least two to one.
U.S. Pat. No. 3,398,149 discloses a process for preparing adenine by heating formamide with a member selected from the group consisting of phosphorous trichloride, phosphorous oxychloride, phosphorous pentoxide, polyphosphoric acid, pyrophosphoric acid, tetrachloropyrophosphoric acid, thionyl chloride, sulfuryl chloride, chlorosulfonic acid and tosyl chloride within the range of from about at 70.degree. C. to about 200.degree. C. in a sealed vessel.
U.S. Pat. No. 3,427,315 discloses a process for preparing adenine or hypoxanthine wherein free formamidine is reacted in a non-aqueous solvent in the presence of ammonia with an .alpha.-amino-.alpha.-cyanoacetic acid derivative of the formula ##STR1## wherein R.sub.2 is hydrogen, formyl, acetyl or propionyl, and R.sub.3 is lower alkoxycarbonyl or carbamoyl.
U.S. Pat. No. 3,671,649 discloses a method of producing adenine and/or 4,5-dicyanoimidazole and derivatives thereof by reacting diaminomaleonitrile or diaminofumaronitrile with an amidine salt in an organic medium.
U.S. Pat. No. 4,059,582 discloses a process for preparing adenine by reacting at least one member selected from the class of diaminomaleonitrile and diaminofumaronitrile, a formic acid derivative and at least one member selected from the class of ammonia and ammonium salts in the presence or absence of a solvent.
U.S. Pat. No. 4,092,314 discloses a process for preparing 4,6-diamino-5-arylazopyromidine from an arylazomalonitrile in the presence of ammonium chloride and formamide. The 4,6-diamino-5-arylazopyrimidine may then be hydrogenated to form 4,5,6-triaminopyrimidine which, when the hydrogenation is carried out in the presence of formic acid or its derivative, gives adenine.
Japanese Patent Publication No. 42-7915 discloses a method of preparing adenine by reacting hydrogen cyanide with ammonia, or an alkali cyanide with ammonium salt and ammonia in the presence of formamide with heating.
Japanese Patent Publication No. 51-26897 discloses a method of preparing adenine by reacting diaminomaleonitrile or diaminofumaronitrile with formaldehyde in the presence of ammonia.
Of particular interest with respect to the present invention is aforementioned U.S. Pat. No. 3,671,649 which teaches a process for producing adenine (and 4,5-dicyanoimidazole) by reacting diaminomaleonitrile (DAMN) or diaminofumaronitrile (DAFN) with an amidine salt having the formula: EQU [H.sub.2 N.dbd.C(R)NH.sub.2 ].sup.+ x.sup.-
wherein R is hydrogen or a methyl group and X is an organic or inorganic acid with heating in an organic medium selected from the group consisting of an aliphatic lower alkyl alcohol having one to four carbon atoms, formamide, dimethylformamide, dimethylacetamide, dimethylaniline, anisole, dioxane and pyridine, and optionally in the presence of an ammonium salt of a lower alkanoic acid. The use of an amidine salt in this process is undesirable because of its relatively high cost. Thus, it would be highly desirable to employ a less expensive substitute for the amidine salt in the practice of the process and still obtain good yields of adenine. In accordance with the present invention, it has been found that N-dichloromethylformamidinium chloride and ammonia can be used in place of an amidine salt in the practice of the prior art process to give good yields of adenine while at the same time affording a cost savings over the use of an amidine salt.